This invention relates to a process for forming fine semiconductor patterns, and more particularly to such a fine pattern forming process which is especially suited for forming patterns with small dimensions around or less than 1 .mu.m.
Hitherto, for forming patterns for magnetic bubble memories and other semiconductor devices, the so-called photoetching technique has been used in which a workpiece is etched through a resist pattern formed thereon. In practice of this photoetching technique, the resist layers are required to have a sufficient thickness to endure during the etching work. For instance, in case a 0.35 .mu.m thick NiFe alloy layer is etched by ion milling, a resist thickness of about 0.7 .mu.m is required. On the other hand, the fact is observed that generally the smaller the resist thickness, the higher becomes the resolution of the resist pattern. Making the best use of this fact, a so-called tri-layer resist process has been proposed in which mask patterns for etching are made by using thin resist layers (J. M. Moran et al: J. Vac. Sci. Technol., 16(6), 1620-1624 (1979)). According to this process, a resin layer is first formed on a workpiece, then an inorganic intermediate layer is formed on said resin layer and a resist pattern is formed on said inorganic layer. The inorganic layer is etched with the resist pattern as a mask, and then the resin layer is etched by, for instance, ion etching using oxygen. In this ion etching, said inorganic layer can act as a mask since this inorganic layer has high durability to ion etching with oxygen. In conducting inorganic layer etching, the resist layers are not required to have a greater thickness than necessary to withstand etching, and usually a small resist thickness on the order of 0.2-0.3 .mu.m is used.
Relating to the inorganic layer, Moran et al proposed an SiO.sub.2 layer formed by CVD (chemical vapor deposition) while Endo et al disclosed an Si layer formed by vacuum deposition (see A Collection of Papers Presented at the 28th Conference of the Japan Society of Applied Physics, 1981, p. 370). These proposals, however, have drawbacks in that an evacuating equipment is required and that the working process is prolonged.
To avoid these problems, a method using an SiO.sub.2 layer formed by spin coating has been proposed (Matsui et al: A Collection of Papers Presented at the 29th Conference of Japan Society of Applied Physics, 1982, p. 357). According to this method, an SiO.sub.2 layer can be obtained by spin coating a monomolecular type organosilicon compound and further applying a heat treatment, and the process is greatly simplified. However, the SiO.sub.2 layer obtained from this method is not quite satisfactory in adhesion to the underlying resin layer and the top resist pattern. In case, for instance, a polyimide resin, which is a heat-resistant high polymeric resin, is used for the resin layer, the SiO.sub.2 layer formed thereon by said method proves to be liable to cracking and no good layer can be obtained. Also, when a novolac resist AZ-1350-J (Shipley Company) is used as resist, the obtained resist layer is found to be poor in adhesion to the underlying SiO.sub.2 layer formed by said method, resulting in separation of the resist pattern. Further, since the monomolecular organosilicon compounds are easily hydrolyzed, a risk is great of the coats being contaminated by alien matters (hydrolyzates).